Method of preparing finely-divided metals or metal-metal compounds and resulting product



' limits of operation.

pear from the following disclosure and Patented Feb. 10, 1931 UNITED STATES PATENT OFFICE WILLIAM G. WILSON, 0F HYDE PARK, MASSACHUSETTS, ASSIGNOB, TO WILLIAM C.

WILSON, OF BOSTON, MASSACHUSETTS,'TRUSTEE METHOD OF PREPARING FINELY-DIVIDED METALS OR METAL-METAL COMPOUNDS 1) RESULTING PRODUCT v No Drawing.

This invention relates to a method for the preparation of metals and alsometal-metal compounds or alloys in a finely divided or colloidal or atomic state, and to the product or products resulting from the application of the invention.

In the several arts where it is found con-' venient or necessary to prepare and use metals in a fine state of subdivision, it is frequently desirable that the sizes of the individual particles may be of an extremelysmall order,-approaching colloidal dimensions or even molecular proportions, if these were possible of attainment. It is usually preferable that such sizes may, to some extent at least, be subject to controlarrd that the range of sizes manifested by a giverfquantity may be within predetermined limits. It is ordinarily further desirable that the metal shall be relatively pure, or of predetermine composition, and sometimes that it shall be.

in a stable or (for some prposes) unstable condition. Numerous specialirequirements of composition and of the physical and chemical properties of the product may be desirable in given instances of use. But such control of size, composition and condition of finely divided metals have not heretofore been attained and metallic powders which have been obtainable have been of uncertain properties and qualifications in these respects.

Accordingly, it is an object of this invention to provide a method which shall'lead to the obtainment of a. product or products manifesting properties as above indicated, and subject to control within predetermined Other objects will apclaims.

The invention broadly includes the discovery that certain metals (or metal-metal compounds or alloys thereof) may be prepared in a fine degree of subdivision (the size of the individual particles being susceptible of control and including substantially colloidal or -molecular dimensions) by subjecting a compound of the same under appropriate conditions of dispersion or solution in a reaction ,medium, typically water, by effecting reaction therewith of a second or precipitant Application fil ed March 20, 1929. Serial no. 348,660.

metal, in free, finely divided condition, which is capable of reducing the compound, e. g as by exhibiting a greater ele'ctromotive force, and characterized by controlling the size or sizes of the metal liberated by the size or sizes in which the particles of the second or precipitant metal are brought into the reaction.

i The compound of the metal to be precipitated is completely and uniformly distributed throughout the reaction medium, preferably by solution therein. An especially favorable form of carrying out the invention is, for example, to employ a salt of the metal, and to dissolve the same in water to form an aqueous solution.

The precipitant metal is reduced to a fine state of mechanical subdivision, in ways appropriate to the characteristics of the metal, and which are well known.

others may be melted and sprayed as finely divided globules into a cooling medium, while still others may be distilled and the vapors condensed. Still other methods of reducing the state of subdivision of the precipitant metal will readily suggest themselves, such as crushing, impact, electrolytic deposition and the like. Zinc, for example, which is especially suitable, may be distilled and the fumes condensed to form zinc dust, which is a readily obtainable commercial product.

The precipitant metal may be used in the dry powdered condition of the a desired particle size, but is ordinarily more conveniently manipulated in the form of a liquid suspension, such as water or a solution of one of its salts.

The solution containing the metal to be precipitated and the liquid suspension of the precipitant metal may be brought together in either order of addition of the one to the other, according to the characteristics of the product required. For the purpose of producing the liberated metal in the free and pure condition, it is preferable to add the suspension of the precipitant metal to the solution containing the metal to be precipitated, which insures a preponderate concentration of the latter, substantially through- V mentioned.

The amounts of precipitant metal and metallic compound employed may be in equimolecular or-chemical proportions, or may be varied from these, as experience and-the properties of the resultant product may dictate. Thus, an insufficiency of the precipitant metal mag leave some of the compoundunreduced or ut partly reduced. An excess of the precipitant metal on the other hand, is sometimes found to react with the metal of the reduced compound to form one or more metal-metal compounds or alloys of definite chemical composition and unique properties. Accordingly, the metal of the compound may be precipitated alone and in pure condition,the purity of the precipitated metal being enhanced either by employing less than a chemical equivalent of the recipitant metal or by employing 'a 'precipltant metal which does not react with the metal to be precipitated to form alloys or direct chemical combinations therewith, or by completing the reaction with such a metal. Likewise, by employing a chemical equivalent, or more, of a prec1pitant metal which is directly reactive with the metal to be precipitated, the composition of the precipitated metal may be governed by the amount and condition of the precipitant metal added. Moreover, the degree of fineness or colloidal or molecular subdivision of the liberated metal is found to be in general smaller than of the precipitant metal but proportionately related thereto.

The invention is generally applicable for the preparation of finely divided metals'or colloidal suspensions thereof, i ther in the pure, elementary condition orl in the form of metallic compounds or alloys of predetermined composition. It is necessary that the metal to be precipitated shall be, effectively, below the metal to be used as the precipitant, in the ele'ctromotive series of the elements. It is also practically essential that the initial compound of the metal to be reduced and the reaction product of the precipitant metal shall be soluble in the medium employed. This usually leads to the use of a salt of the metal freely soluble in water as the reaction medium. For the preparation of metal-metal compounds containing the precipitant metal and the precipitated metal, it is found preferable to add the precipitant metal not only in finely divided form but in suspension in a solution of one of its salts. It maybe still further activated thereby, as by a preliminary boiling of the suspension, as will hereinafter a' pear. However, further conditionsmay be impressed thereon, such as freedom from dissolved gases, the provision of suitable reaction temperatures, conditioning reagents such as acids or alkalis, and the addition of liquids or gases thereto, calculated to control the reaction or to be (selectively) absorbed upon the liberated metal and thus to arrest or retard crystal growth of the liberated metal. The latter function may be analogous to and substituted by the addition of a protective colloid. However, it is desirable that the medium berelatively fluid and such as to permit the rapid and uniform intermingling of the several reagents throughout its volume. a

A' specific and representative instance of the application of the invention will be described as carried out for the preparation of finely divided (colloidal) copper from an aqueous solution of one of its saltsemploying zinc powder or dust as the precipitant metal.

The compound of copper may conveniently be any soluble salt (commercial or chemically pure) such as the sulfate, which may preferably be dissolved in water to form a uniform solution.

The zinc dust or powder (which may be the commercial product or further purified, if desired) is reduced to a predetermined size or order of sizes as by passing through a screen, e. g., 325 meshes per linear inch, corresponding to a maximum particle size of 1/650 inch diameter or approximately 4 x 10- mm. or 40 or by flotation, air separation, or the like, is then stirred with water until thoroughly wet'and carried into the condition of a relatively uniform suspension therein.

The components of the solution and suspension as thus prepared, may be in substantially equivalent molecular proportions, as follows :1000 grams CuSO 5H O to 4000 grams water; 266 grams commercial zinc dust v to 250 grams water; the metals being present in substantially equimolecular proportions, corrections being applied for impurities such as zinc oxide, water of crystallization, etc.

The two liquids are then mixed together rapidly and with continued agitation of the whole until reaction, which takes place rapidly, is complete.

The metathetical reaction may be represented thus the deposit of copper which may be produced thereby, as indicated by the following table of results which have been obtained in this manner It is thus found that the degree of subdivision and dissemination or dispersion of the particles of the precipitant metal are directly determinative of the size of particles or aggregates into which the liberated metal shall be formed upon its reduction and conversion into elemental form. This effect is further enhanced by a rapid or instantaneous intermingling of the precipitant metal with the compound to be reduced. This result may be attributed to the instigation of a multiplied number of reaction nuclei at which the reduction of the metal compound takes place and hence a multiplied number of particles of the reduced metal, which are of correspondingly less individual volume and mass than those of the precipitant metal.

The precipitant metalin the instant case, zinc dust-simultaneously goes into solution as the sulphate. Since both metals are present in equimolecular proportions, the reaction is substantially complete and the zinc dust is dissolved aszinc sulphate.

The concurrently precipitated deposit of colloidal copper, as thus provided, is washed free from electrolyte'preferably without exposure to oxidation and may be converted into a more permanent colloidal solution or suspension by the addition of a suitable protective agent, such as a dilute solution of glue, casein, or other substance having similar properties. In this form, the colloidal suspension may be preserved indefinitely without deterioration, and is especially suitable for those purposes to which such metal powders are or may be applied.

For example, the product is especially suitable for applying as a metallic surface coating to paper, the mixture being painted upon the surface and allowed to dry, followed by burnishing the. deposited layer of metal particles, as by calendering. By this operation the individual particles are laid flat and joined to adjacent particles to form a continuous metallic sheet, of extreme thinness but manifesting all of the properties characteristic of metallic surfaces in mass. The glue casein or gum arabic, if added, serves as an adhesive to retain the coating in association with the paper sheet, but this may be dispensed with if the surface and metal are capable of sufficient adhesion.

With the proportions above alluded to, in which the amount of zinc used is substantially the molecular equivalent of the copper to be precipitated, it is found that the copper precipitate contains a small proportion of zinc, and that this zinc content is not susceptible of removal, as by leaching with acids, without also dissolving or otherwise affecting the copper. Where such combination of the precipitant metal may be objectionable anda purer grade of metallic copper is desirable,

the amount. of precipitant metal initially i added may be reduced to somewhat lessv than a molecular equivalent (e. g. 90%) and the process conducted as above described, whereupon an excess of the metal to be precipitated is left in solution, butthe deposited metal is substantially pure. At this stage, the precipitate may be washed free from the supernatant solution, as before, or the precipitation (of copper) may be completed by the addition of a second metal (which does not tend to react or alloy with the metal to be precipitated such as magnesium or aluminum) in any amount substantially equivalent to or greater than the residual molecular proportion of copper, thereby precipitating the copper without combinationof the precipitant metals (e. g. zinc, aluminum, or magnesium). It is to be especially remarked that the copper deposit obtained in this manner is particularly stable and may be dried in the air whereas if an excess of zinc is at any stage contacted with the solution to form Cu Zn, or other copper-zinc compounds (as hereinafter pointed out), even though temporarily only the resultant deposit is unstable and rapidly deteriorates, as by oxidation. Accordingly, the complete precipitation may be effected with a non-reactor with copper, such as magnesium or aluminum, but the preliminary use of zinc is not detrimental and is economical and convenient to obtain. 7

It is further found, as apart of this invention, that if the precipitant metal, such as the zinc in the foregoing example is susceptible of alloy-formation with the metal to be precipitated, such as copper,the addition of an excess quantity of zinc to the copper solution in the above described procedure (as by adding the copper solution slowly to the zinc suspension) will precipitate. a compound metal or alloy containing both metals, in e ,and can not, for example, be preferentially dissolved by acid without chemical alteration of the compound occurring simultaneously therewith. Such metal-metal com- 1 pound or alloy of zinc and copper and the I pound characteristically exhibits uniformity of properties and composition throughout the mass. It is therefore deemed to be an alloy, or direct chemical compound of the two metals, associated by virtue of the chemical reaction by which it is produced in contradistinction to the usual association of such metals in the free condition by melting.

It is now further found that :if-the' finely divided'precipitantcmetal (zinc) is given a preliminary treatment with one of its salts in ionized condition, (as for example an aqeous solution of zinc sulfate it becomes ionized and more reactive with the precipitated metal (copper). When used in sufficient proportions, the zinc as thus prepared will combine with the copper to form the compound corresponding to the formula CuZn. Moreover, if both solutions (the zinc sulfate suspension of zinc and the copper sulfate solution) are boiled and. mixed at the boiling temperature, a compound of the formula GuZn is formed and precipitated.

For example: 10 grams of GuSO 5H O are dissolved in 50 c. c. of cold water and a suspension is prepared of 6 grams of zinc dust in 20 c. c. of a 15% solution of ZnSO which is boiled vigorously for a few minutes and then allowed to cool. The copper sulfate solution is then stirred into the suspension of zinc. The precipitate is then treated with sulfuric acid (not in excess of 10% concentration) to dissolve the excess of zinc and the supernatant solution withdrawn, leaving a fine deposit of metal-metal compound having a composition corresponding to the formula CuZn and unafieoted by sul- I furic acid of concentration up to 10%.

If the same procedure is followed,-employing approximately 8 grams of zinc dust, and the solutions maintained at the boiling temperature during admixture, and cooled to room temperature before treating with sulfuric acid, the product obtained has a com.-

position corres onding to the formula CuZn This compoun is not affected by 2% sulfuric acid,,but if treated with a 5% to 10% so1ution of sulfuric acid, an integral atomic proportion of its zinc component is removed, giving a product of the formula Cu Zn A combination of these procedures may be effected (either to make possible the use of a-'-smaller excess of zinc required or to pro- 'i.' ;d i .i ee compounds of hi her zinc content as indicated above) by adding the cold copper suland thereafter boiling the mixture to pre-.

cipitate the copper-zinc compound, the chemical composition of which is controlled by the a relative proportions of the two metals present up tothe chemical compound having the composition CuZn If now, the copper-zinc alloys or compounds as thus produced are brought into contact with more copper sulphate in solution, the zinc component is displaced successively and relatively pure copper is ultimately precipitated. v

It has been observed, however, that the copper produced from, or under conditions tending toward the formation of the copperzinc compound is especially unstable and extremely reactive chemically, whereas copper produced by direct displacement from its salt to the solid, elementary condition is relatively stable. For this reason, as above indicated, for the production of a stable copper precipitate the zinc suspension is added to the copper solution and the reaction mixture is continuously and vigorously agitated. On the other hand, if the copper-zinc compound is desired the copper solution may be added to the zinc suspension, or the relative concentrations of the two may be apportioned, while if reactive copper is desired, the'copper-zinc compound may be made first and then reduced to the reactive copper or copper-copper compound by treating with additional copper sulfate solution.

This distinction between the stable and unstable cop er may be noted in the reactivities of the sta le copper precipitated by a nonreactive metal, such as aluminum and unstable copper precipitated by a metal reactive therewith, such as zinc.

For example: 10 grams CuSOJjH O may be dissolved in 50 c. c. water, and a chemical equivalent of powdered aluminum suspended in a solution contaiing 15% Al (SO The copper sulfate solution is then added slowly and with stirring to the suspension of aluminum, the precipitated molecular equivalent of copper is Washed and treated with a suspension of 10 grams of zinc dust in a 15% solution of zinc sulfate and boiled for one hour. The precipitate, upon separation, and washing in 12% H 30 upon analysis gave the following composition:

Cu7 l.5%Zn25.5% Cu Zn Upon conducting the same procedure with a chemical equivalent of zinc in15% solution of ZnSO instead of aluminum and alumi- V Cui9.0% Zn51.0% GuZn This still further demonstrates the dilferent characteristics and properties of the active or unstable precipitated metal when the 5 vessels, wharves and the like.

precipitant metal is reactive therewith, and the stable metal produced when the precipitation is effected by a non-reactive metal.

The copper-zinc compounds thus obtained are distinguished by uniform and distinct coloration, especially after burnishing to a polished surface,that of the formula CuZn having a color and lustre of pale gold, while that of the formula C11 Znis deep gold, Cu Zn is medium gold, and the compound CuZn is silvery gray. The color and properties of all three are entirely different from those of mechanical admixtures of copper and zinc even though of a like degree of subdivision, and burnished to a polishedsurface in like manner.

Again, if the copper-zinc alloy or compound is added to a solution of a salt lower in the electromotive series than zinc, the zinc of the alloy will displace such metal from its salt and be in turn replaced thereby in the alloy,-

Oll Zll CugSn OII ZII Gu Zn+ CoSO, Cu Co ZnSO, Cl1 ZI1+Pb(C H O 2 Cu Pb Zn 1-1 0 2 By analogy, when the compound is contacted with a copper salt, a similar reaction may occur:

Cu Zn 01101 0112011 ZnCl the copper-copper compound being unstable.

The finely divided metals as thus produced may be fabricated into continuous sheets or solid bodies or molded for various purposes.

It is clear that metals or metal-metal compounds obtained by the present invention are adaptable for many purposes and the specific applications for which they may prove especially suitable arecommensurate with the importance of phenomena attributable to the'presentation of extensive surfaces relative to mass and with the multifarious phenomena and practical usages of colloidal materials generally. Thus, finely divided copper is useful for coating paper, as above mentioned, and also-textiles and other materials, and may exhibit a dull or lustrous metallic sheen. In other words it may comprise a continuous'or permeable surface film,as by deposition only or by burnishing the deposited layer. Again, the finely divided material may serve, by admixture with appropriate vehicles, as the pigment of paints, and like coating materials. For example, copper is known to have a marked bactericidal value and is employed in the form of sheets or of its chemical compounds for this purpose. A paint containing finely divided metallic copper would accordingly be expected to find extensive use for protecting the underneath surfaces of Such at paint This application might be secured directly in the precipitation procedure by employing a protective colloid as above alluded to, which would also serve as a paint vehicle. Again, the catalytic properties of the metals and of the metal metal compounds (stable and unstable) present a prolific field of usefulness towhich the products derived in accordance with this invention areespecially suited.

Other adaptations and applications of the invention may-and ordinarily willbe made in the practical utilization of the same in the several arts and various substitutions and proportions may be adopted for the obtainment of specific results in the ultimate product, but the present disclosure is deemed to embrace a subject matter which is broadly new and such applications and substitutions are tobe understood as comprehended in the above description and included within the following claims.

is a continuation in part of my application Serial No. 17 5,934, filed March 16, 1927 I claim:

.1. A method for the preparationof ametal in finely divided condition, which comprises reducingthe metal from one of its salts by effecting intimate contactof the latter in av dispersed state with a precipitant metal, said precipitant metal being characterized by a chemical reactivity sufiicient to liberate the metal to be reduced, and controllinglthe particle size of the liberated metal by t e degree of comminution, less than 40 mu, of the precipitant metal.

2; A method for the preparation of a metal in ionized condition which comp-rises suspending the same in finely in an aqueous solution of one of its boiling the resulting suspension.

3. A method for the preparation of a metal in finely divided condition, which comprises dissolving a salt of the same in anappropriate solvent, reducing the salt to liberate the metal component thereof with a second metal in ionized condition, and controlling the degree of fineness of the liberated metal by the fi eness, less than 40 mu, of the precipitant etal employed.

salts, and

divided condition 4. A method for the preparation of a metal in finely divided condition, which comprises dissolving a salt of the same in an appropriate solvent, reducing the salt to the free metal by effecting intimate contact of the same with a precipitant metal, the latter being characterized by being above the metal to be reduced, in the electromotive series, and present in a finely divided condition, and displacing the reaction products. from contact with the liberated metal 'by means of a protective colloid.

5. A method for the preparation of a metal in finely divided condition, which comprises dissolving a salt of the same in an appropriate solvent, and reducing the salt to the free metal by effecting intimate contact of the solution witha substantially equivalent quantity of a finely divided second metal, less than 40 um, the latter being characterized by being above the metal to be reduced in the electromotive series and non-reactive therewith.

6. A method for the preparation of a metal metal compound or alloy in a finely divided condition, which comprises dissolving a salt of one of the metals in an appropriate solvent, and reducing the salt by effecting intimate contact of the same with a finely divided second metal, in predetermined molecular uantity in excess of its chemical equivalent 0 the metal to be precipitated, and characterized by being above the metal to be reduced in the electromotive series and reactive to form a chemical association with the liberated metal.

7. A method for the preparation of a metalmetal compound in. a finely divided condition, which comprises dissolving a salt of one of the metals in an appropriate solvent, and reducing the salt by eflecting intimate contact of the same with a second metal in the form of finely divided particles approachingcolloidal dimensions and, in ionized condition,

'in the presence of a solution of its salt and in a quantity in predetermined excess of a chemical equivalent of the first, the latter being characterized by being above the metal to be reduced in the electromotive series and re active to form a chemical association with the liberated metal.

8. A method for the preparation of a metalmetal compound or alloy inva finely divided condition, which comprises dissolving a salt of one of the metals in an appropriate solvent, and reducing the saltby efi'ecting intimate contact of the same with a metal-metal compound, the latter being characterized by containing a metal above the metal to be reduced in the electromotive series and present in finely divided condition.

9. A method for the preparation of a free metal in a finely divided condition, which comprises dissolving a salt of one of the metals in an appropriate solvent, and reducing the salt by efi'ecting intimate contact of the same with a second metal, in a predetermined quantity less than a chemical equivalent of the first, the latter being characterized by being above the metal to be reduced in the electromotive series and present in finely divided condition, less than 40 mu.

10. A method for the preparation of a metal-metal compound or alloy in a finely divided condition, which comprises dissolving a salt of one of the metalsin an appropriate solvent, and reducing the salt by efl'ecting intimate contact of the same with a second metal, the latter being characterized .by being above the metal to be reduced in the electromotive series capable of association with the first, ionized in the presence of a solution of one of its salts, and present in finely divided condition, less than 40 mu, followed by separating the liberated metal from other reaction products.

11. A method for the preparation of a metal in a finely divided condition and a relatively stable state, which comprises dissolving a salt of one. of the metals in an appropriate solvent, and reducing the salt to the free metal by efl'ecting intimate contact of the same with a second metal, in a predetermined quantity less than a chemical equivalent of the first, the latter being characterized by being above the metal to be reduced in the electromotive series and present in, finely divided condition, followed by the ad-l dition of a second metal characterized by be-i ing above the metal of the salt, in the electromotive series, and substantially without tendency to combine with the metal to be precipitated.

12. A method for the preparation of a, metal-metal compound or alloy in a finely d1- vided condition, which comprises dissolving a salt of one of the metals in an appropriate solvent, preparing a suspension of a second metal, in finely divided condition less than 40 mu, in a solution of one of its salts, sa1d second metal standing above the first in the electromotive series, mixing the solution and suspension as thus prepared, 1n appropriate proportions at ordinary temperature, and thereafter heating the mixture to bolling.

13. A method of making copper-zinc cempounds, which comprises the steps of bOlllHg a suspension of finely divided ZlIlC 1n a solution of one of its salts, and thereafter slowly adding a solution of a copper salt thereto.

14. A method of making copper-zmc compounds, which comprises the steps of bollmg a suspension of finely divided zinc in a solution of one of its salts, and thereafter slowly adding a solution of a copper salt thereto, while. maintaining the reagent solutlon and mixture at the boiling point.

15. A metal-metal compound, characterized by a fine state of subdivision and having a chemical composition indicated by the formula Cu zn.

16. A metal-metal compound, characterized by a fine state of subdivision and having a chemical composition indicated by the formula CuZn.

17 A metal-metal compound, characterized by-a fine state of subdivision and havin a chemical composition indicated by the formula CuZn 18. A metal powder, characterized by a state of colloidal division and containing tw metals, chemically combined, the second meta being above the fi.st in the electromotiv series.

19. A 'metal powder characterized by state of colloidal division and by containin two metals in atomic proportions in alloyassociation without fusion.

20. A method for the preparation of a metal in ionized condition, which comprises suspending the same in finely divided condition, less than mu, in an aqueous solution of one of its salts.

21. A method for the preparation of a metal in ionized condition, which comprises suspending the same in finely divided condition, less than 40 mu, in an aqueous solution of one of its salts, and heating the resulting suspension.

22. A metal powder characterized by containing two metals in substantially complete chemical combination without fusion in approximately atomic proportions by weight.

Signed by me at Boston, Massachusetts, this 19th day of March, 1929.

WILLIAM G. WILSON. 

